This invention relates in general to liquid filter systems and, more specifically to a system for filtering particulate material from a liquid stream providing improved filter life and automatic high efficiency back flushing without interrupting flow through the system.
A great many small rural communities presently use surface water from streams or rivers for their municipal drinking water supply. Due to perceived increases in water pollution, increasingly stringent limits are being required on chemical contaminates and parasites in drinking water. This is requiring increased water treatment, including greater removal of particulate contaminates from the water. In small water treatment plants used by small communities, low cost and low maintenance are required if new water treatment plants are to be affordable.
Many older water treatment plants use dual-media sand filtration systems that are no longer acceptable under the new water quality standards. In some cases, these systems can meet the standards, but only through the use of properly mixed polymer chemical filter aids. The required expensive and complex polymer chemical mixing equipment requires constant attention, since the amount of the chemicals being added to raw water must be frequently readjusted to match the continually changing chemistry of the water being filtered. Most small rural water districts cannot afford to both purchase these sophisticated dual-media systems and provide the full time engineers required to operate and maintain these systems.
Many small rural water districts are trying to avoid these high costs by merging with other districts or drilling wells. Where the costs of such interconnections or wells is excessive, under present regulations, they may install slow sand filters. Most slow sand filters require minimum maintenance and can operate for weeks without cleaning.
Unfortunately, recent particle count studies show that both dual-media and slow sand filters fail to meet water quality standards for hours, several days or even months after each backwash cleaning. Contaminates have been found to pass through a sand filter whenever water flow rates are changed and whenever the pump is stopped and turned on again. In order to meet standards, it may be necessary to pump filtered water to waste after every backwash cycle, disposing of thousands of gallons of water, until the filter "ripens" or compacts.
Thus, there is a continuing need for improved liquid filtering systems, especially for use in small water treatment facilities, that will be highly efficient, require little or no monitoring, will automatically backwash as required without interrupting overall water flow and will not waste excessive liquid during the back flush cycle.